1. Field of the Invention
The present invention relates to a flame-retarding composition for polymers, copolymers and mixtures thereof, such as polyolefins, polyamides, etc., as well as epoxy resins, polyester resins, and the like. The invention also relates to a process for the preparation of said composition, as well as the polymers, copolymers, mixtures thereof, thermoplastic and thermosetting resins, and various polymeric materials such as paints, fabrics and the like, which are rendered self-extinguishing by means of said flame-retarding composition.
2. The Prior Art
As is known, a polymeric material is generally caused to become "self-extinguishing" or "anti-flame" or "flame-resistant" by the addition of particular "anti-flame" or "flame-retarding" agents, that can just impart the polymer substance the self-extinguishing characteristics required. Such anti-flame agents are constituted by organic halogenated, usually brominated substances, metal compounds (in particular oxides, such as for instance antimony trioxide), phosphorus and derivatives thereof (such as for instance red phosphorus, ammonium polyphosphate, organic phosphoric esters), various nitrogen-containing compounds (such as for instance urea, dicyandiamide, melamine), and still other ones. As is known, in some cases, in order to achieve the desired self-extinguishing characteristics in a polymer, there are also used two or more different anti-flame products associated with one another, both to exploit in combination anti-flame characteristics and/or "functions" that are specific of the individual products, and to realise given "synergistic" or "combined" effects, and also to avoid adding too high amounts of an individual anti-flame agent, which though being necessary to achieve the desired self-extinguishing level of the polymer would involve an alteration or degradation of said polymer, due to the very characteristics of the anti-flame agent used.
The formulations of polymer articles having self-extinguishing and intumescent characteristics comprise the polymer and at least two basic additives: a phosphorus-containing one, and a nitrogen- and/or nitrogen/carbon-containing one.
A typical example is ammonium polyphosphate which, utilised in the right concentration, imparts the polymer composition class U L 94 VO self-extinguishing characteristics.
Other compounds that can impart self-extinguishing characteristics are piperazine phosphates (U.S. Pat. No. 3,810,850).
However, the aforementioned compounds prove poorly suitable for use if they are utilised in high-temperature processes or for long periods (polyolefins are a typical example).
The compounds described in EP 84105667.4, useful for use at high temperatures, namely piperazine diacid pyrophosphate, overcomes the aforesaid limits, being provided with high thermal stability and also with good self-extinguishing and intumescent properties.
The effectiveness of the product as concerns the self-extinguishing capacity is markedly improved by the addition of synergistic components containing nitrogen and/or phosphorus (melamine, melamine phosphates and pyrophosphates, ammonium polyphosphate, products of ethylenurea and formaldehyde condensation) and minor additives (silica, silicic acid, and titanium dioxide). The so formulated preparations perform well as concerns self-extinguishing capacity (UL 94; total combustion time; oxygen index).
However, the same patent reports that the conversion yields as concerns the production of the additive are very low (53%).
It is also known that with the anti-flame compositions of the known art there can often take place losses due to extraction and/or solubilisation of the anti-flame agents incorporated in the polymeric materials, with ensuing loss of the flame-retarding power, efflorescences on the material, etc.